The present invention relates generally to medical stimulators, and more specifically to implantable cardioverters.
It has been recognized for some time that in delivering a cardioversion pulse, it is desirable to synchronize the pulse to a sensed ventricular tachyarrhythmic depolarization. A device for accomplishing this synchronization is disclosed in U.S. Pat. No. 3,527,228 issued to McLaughlin.
Incorporation of such a synchronization circuit into an implantable defibrillator is disclosed in U.S. Pat. No. 3,738,370 issued to Charms. A later disclosure of a synchronous atrial cardioverter may be found in U.S. Pat. No. 4,572,191, issued to Mirowski et al.
Detection of a tachyarrhythmia episode and thereafter triggering a tachyarrhythmia treatment regimen is also disclosed in U.S. Pat. No. RE 30,387 issued to Denniston et al. Later disclosures of tachyarrhythmia detection methodologies may be found in U.S. Pat. No. 4,403,614 issued to Engle et al., U.S. Pat. No. 4,375,817 issued to Engle et al., U.S. Pat. No. 4,493,325 issued to Hartlaub et al., U.S. Pat. No. 4,384,585 issued to Zipes and U.S. Pat. No. 4,552,154 issued to Hartlaub, all incorporated herein by reference in their entireties.
In addition to delivery of large amplitude defibrillation and/cardioversion pulses, treatment of tachyarrhythmia episodes by means of overdrive pacing has also been extensively researched. One such overdrive pacemaker is disclosed in U.S. Pat. No. 4,577,633, incorporated herein by reference in its entirety. An earlier disclosure of a microprocessor based pacemaker capable of overdrive pacing may be found in U.S. Pat. No. 4,485,818, also incorporated herein by reference in its entirety. In overdrive pacing, the pacemaker senses the rate of the detected tachyarrhythmia and generate pacing pulses at a higher pacing rate, thereafter gradually reducing the pacing rate in an attempt to return the heart rate to a normal range.